The present invention relates to vacuum cleaners. More specifically, the invention relates to self-propelled vacuum cleaners.
Known self-propelled vacuum cleaners include an electric motor disposed in the suction nozzle or base of the cleaner for driving a set of driven wheels. The drive motor exerts a driving force on the driven wheels in a direction of movement of the suction nozzle base desired by the operator. A detector is provided to control the direction that the drive motor will drive the wheels. One known detector located in the handle of the vacuum cleaner includes a switch having three positions to control the direction of rotation of the motor. If an operator pushes the vacuum cleaner forward, the switch is forced into a first end position under the influence of the friction between the switch and the surface to be cleaned. With the switch in the first end position, the motor drives the driven wheels with a substantially constant speed in a forward direction. If the operator pulls the vacuum cleaner backward, the switch is forced into a second end position under the influence of the friction. In the second end position the motor drives the driven wheels with a substantially constant speed in a backward direction. If the user keeps the suction nozzle stationary, the switch is displaced to an intermediate position disposed between the two end positions, where the drive motor does not rotate.
The known detector includes helical springs to urge the detector into the intermediate or neutral position after the user has stopped pushing or pulling on the handle of the vacuum cleaner. The use of such helical springs has resulted in problems including overshoot of the neutral position, high acceleration when the force is applied or removed, and ringing of the components inside the handle. Ringing can result from the helical spring vibrating in a direction perpendicular to its longitudinal axis resulting in the spring contacting its housing, i.e. the handle. This vibration can result from movement of the motors in the vacuum cleaner transferring forces to the handle.
Furthermore, the use of a spring in a system of connected bodies of results in periodic motion. In a vacuum cleaner having a spring that urges a detector into a neutral position after the user has stopped pushing or pulling on the handle, a spring not exhibiting proper damping characteristics may result in “overshoot” after the force, which is supplied by the operator, has been removed. The portion of the handle that is connected to the spring will attain a velocity such that the spring will move out of equilibrium. Since the motor is in neutral only when the spring is in equilibrium, when the spring “overshoots” equilibrium the sensor delivers a message to the motor to drive in the opposite direction from the direction the motor was just driving in. Such overshoot can result in jarring at the motor and in the vacuum cleaner as a whole.
Accordingly, it is desirable to provide a mechanism to urge the drive control mechanism into a neutral position while eliminating the above-mentioned problems exhibited in the prior art.